Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $152.67   11.478%   $170.1935   $170.19   $170.20   $170.20  
  Purchase #2 $161.75   9.530%   $177.1648   $177.16   $177.15   $177.20  
  Purchase #3 $156.81   9.632%   $171.9139   $171.91   $171.90   $171.90  
  Purchase #4 $181.60   10.407%   $200.4991   $200.50   $200.50   $200.50  
  Purchase #5 $163.58   3.495%   $169.2971   $169.30   $169.30   $169.30  
  Purchase #6 $117.94   6.310%   $125.382   $125.38   $125.40   $125.40  
  Purchase #7 $47.58   10.634%   $52.6397   $52.64   $52.65   $52.60  
  7 purchase totals = $981.93       $1,067.0901   $1,067.08   $1,067.10   $1,067.10